Abstract:
Changes in soil water content with increasing ambient relative humidity was examined using model
soils prepared by mixing silica sand with different types of organic matter and different types and con tents of clays. In this study, we used commercially available hydrophobic and hydrophilic organic mat ter, and kaolinite and montmorillonite under four levels of relative humidities. Soil water content of all
the soils increased with increasing relative humidity. Hydrophilic organic matter, which is reported to
decrease the wettability of soils, was found to increase the absorption of water into soils in the vapor
form. In model soils without clay, hydrophobic organic matter, which is reported to impede water entry
in liquid form (water repellent), was found to have little or no effect on water vapor absorption. In con trast, when the model soils containing 1–2% clays, hydrophobic organic matter slightly decreased the
water vapor absorption. Montmorillonite containing samples showed higher water vapor absorption,
and therefore, higher water contents compared with those containing kaolinite. The difference in water
content between samples containing montmorillonite and kaolinite increased with increasing clay con tent. Increase in clays with high water absorption capacity was found to make the clay effects on water
vapor absorption prominent and to hinder the effects of hydrophobic or hydrophilic organic matter on
water vapor absorption. The absorption of water into soils in vapor form was found not to be compara
